docs: def Morton(rhol, rhog, mul, sigma, g=g):
      r'''Calculates Morton number or `Mo` for a liquid and vapor with the
      specified properties, under the influence of gravitational force `g`.
  
      .. math::
          Mo = \frac{g \mu_l^4(\rho_l - \rho_g)}{\rho_l^2 \sigma^3}
          
      Parameters
      ----------
      rhol : float
          Density of liquid phase, [kg/m^3]
      rhog : float
          Density of gas phase, [kg/m^3]
      mul : float
          Viscosity of liquid phase, [Pa*s]
      sigma : float
          Surface tension between liquid-gas phase, [N/m]
      g : float, optional
          Acceleration due to gravity, [m/s^2]
  
      Returns
      -------
      Mo : float
          Morton number, [-]
  
      Notes
      -----
      Used in modeling bubbles in liquid.
  
      Examples
      --------
      >>> Morton(1077.0, 76.5, 4.27E-3, 0.023)
      2.311183104430743e-07
  
      References
      ----------
      .. [1] Kunes, Josef. Dimensionless Physical Quantities in Science and 
         Engineering. Elsevier, 2012.
      .. [2] Yan, Xiaokang, Kaixin Zheng, Yan Jia, Zhenyong Miao, Lijun Wang,
         Yijun Cao, and Jiongtian Liu. “Drag Coefficient Prediction of a Single 
         Bubble Rising in Liquids.” Industrial & Engineering Chemistry Research, 
         April 2, 2018. https://doi.org/10.1021/acs.iecr.7b04743.
      '''
      mul2 = mul*mul
      return g*mul2*mul2*(rhol - rhog)/(rhol*rhol*sigma*sigma*sigma)